parser: allow multiple flag values in enum.from() for flag enums (fix #21569) (#21615)

vlib/v/parser/parser.v

@@ -4161,15 +4161,18 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 	isb.write_string('		val := unsafe{ ${enum_name}(input) }\n')
 	if is_flag {
 		isb.write_string('		if input == 0 { return val }\n')
+		all_bits_set_value := '0b' + '1'.repeat(fields.len)
+		isb.write_string('		if input & ~${all_bits_set_value} == 0 { return val }\n')
+	} else {
+		isb.write_string('		match val {\n')
+		for f in fields {
+			isb.write_string('			.${f.source_name} { return ${enum_name}.${f.source_name} }\n')
+		}
+		if is_flag {
+			isb.write_string('			else{}\n')
+		}
+		isb.write_string('		}\n')
 	}
-	isb.write_string('		match val {\n')
-	for f in fields {
-		isb.write_string('			.${f.source_name} { return ${enum_name}.${f.source_name} }\n')
-	}
-	if is_flag {
-		isb.write_string('			else{}\n')
-	}
-	isb.write_string('		}\n')
 	isb.write_string('	}\n')
 	isb.write_string('	\$if input is \$string {\n')
 	isb.write_string('		val := input.str()\n') // TODO: this should not be needed, the `$if input is $string` above should have already smartcasted `input`

vlib/v/tests/enum_flag_from_test.v

@@ -0,0 +1,21 @@
+@[flag]
+pub enum Flag as u8 {
+	flag0
+	flag1
+	flag2
+	flag3
+	flag4
+	flag5
+	flag6
+	flag7
+}
+
+fn test_ok() {
+	a := Flag.from(0b10101110) or { panic(err) }
+	assert a == Flag.flag1 | .flag2 | .flag3 | .flag5 | .flag7
+}
+
+fn test_fail() {
+	a := Flag.from(0b110101110) or { Flag(Flag.flag0) }
+	assert a == Flag.flag0
+}